The importance of desalination techniques to supplement naturally available fresh water for increased residential, industrial, and farming applications throughout the world is well-known. To reduce energy consumption, and thus reduce the cost to produce fresh water, the use of heat contained in a solar pond has been suggested. One approach is disclosed in Israeli Patent No. 67054 which utilizes a flash evaporator operating on hot brine removed from the heat storage layer of a salt water solar pond. As is well-known, a salt water solar pond is a body of water in which a halocline is interposed between a convective upper wind-mixed layer of saline water (i.e., water whose salinity is between about 1 % and 5 %) exposed to the ambient atmosphere, and a lower heat storage layer of concentrated brine. The salinity profile through the halocline increases in a downward direction with a result that the halocline is non-convective and serves as a collector of solar radiation and as an active insulator for the underlying heat storage layer which is heated by direct absorption of solar radiation and by conduction from the halocline.
In Israeli Patent No. 67054, the brine from the heat storage layer is flashed into steam which is then condensed into desalted water in an indirect contact heat exchanger cooled by sea water. The sea water is heated by the condensing steam, and then sprayed over an evaporation pond thus enhancing the evaporation of water from the sea water and increasing the concentration of the brine that collects in the evaporation pond. Concentrated brine from this pond is pumped into the heat storage layer of the salt water solar pond at one end thereof to replace the brine that is removed from the heat storage layer at the other end of the pond, and that is added to the flash evaporator. During its traverse from one end of the pond to the other, the brine is heated by solar radiation.
A major problem with this approach is the inherent instability of the solar pond because of the regular replacement of concentrated brine in the heat storage layer of the pond with fresher water. This creates what is termed a "falling" solar pond. Another problem is that all of the desalted water produced is derived from the heat storage layer; and thus, the production of desalted water is limited.
U.S. Pat. No. 3,868,308 discloses a multi-effect evaporator in which steam from an external source is condensed to desalted water in an indirect contact heat exchanger that is cooled by sea water. Some of the sea water is converted to a vapor by heat exchange process, and this vapor is applied to a succeeding effect which is also cooled by sea water, etc. No specific apparatus is shown or described dealing with condensing the output of the last effect, and no source for steam is shown or suggested. It would be desirable to utilize a salt water solar pond as a source of steam, but the configuration shown in the 1308 patent is not conducive to this particularly because of problems in maintaining the stability of the pond in the face of the withdrawal of hot brine from the pond.
It is, therefore, an object of the present invention to provide a new and improved method of a means for water desalination using a salt water solar pond which overcomes many of the problems of the prior art.